Light emitting diodes, i.e. LED's, have become an increasingly popular source of light for illuminators. The recent developments in LED technology have radically improved the output of the diodes, whereby new application areas have emerged. Indeed, the use of LED's has expanded from the traditional indication purposes to more demanding indoor and outdoor lighting apparatuses.
The improved light output has revealed problems newly associated with LED's. One particular issue is the color distribution in the produced light patter. Color distribution was never considered an issue with traditional LED's because they had relatively low light output. With modern LED's with high light output, however, the distribution of color is a concern as LED's are used to illuminate large areas in indoor lighting, for example. The issue is emphasized when using separate LED's for particular wavelength bandwidths. In indoor lighting applications, for example, it is common to use one LED for each primary color, i.e. three LED's for red, green and blue, respectively. In such a multi-source illuminator it is common that the colors are clearly distinguishable in the light pattern produced, which is not desirable when pursuing light with uniform color.
For managing the color distribution, various solutions have been proposed. An established solution for managing the color distribution of illuminators with an LED light source is to use a plurality special lenses, the incident surfaces of which have been treated such to mix different wavelengths produced by the LED into a light pattern which contains all wavelengths evenly distributed across the pattern.
Another solution is proposed by US 2011/0018016 A1 which discloses an optical surface for producing a desired color pattern. The optical surface according to US 2011/0018016 A1 features a plurality of bulges which extend from an otherwise planar emission surface of a lens. The bulges are used to converge light beams refracting from the emission surface of the lens for controlling the color pattern produced.
The optical surface as proposed by US 2011/0018016 A1 is mainly suitable for controlling the angular color distribution pattern, which does not address the issue of mixing different wavelengths produced by the LED into a light pattern which contains all wavelengths evenly distributed across the pattern.
It is therefore an aim of the present invention to provide an optical surface which when used as an emission surface or as a portion thereof—is able to mix different wavelengths produced into a light pattern which contains all wavelengths evenly distributed across the pattern.